HBO is the original cable network to originate as a non-terrestrial broadcast TV network. HBO went on the air in 1972 and was originally transmitted via terrestrial microwave towers. In 1976, HBO became the first TV network to broadcast its signals via satellite when it showed the "Thrilla From Manila" boxing match between Muhammad Ali and Joe Frazier. In 1986, HBO also became the first satellite network to encrypt its signal from unauthorized viewing. HBO also was one of the first cable TV networks to broadcast an HDTV version of its channel.